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Abstract:

A power semiconductor module includes a housing, a base plate disposed in
the housing, a plurality of substrates mounted to the base plate, a
plurality of power transistor die mounted to the substrates and a
plurality of terminals mounted to the substrates and protruding through
the housing. The terminals are in electrical connection with the power
transistor die. The power semiconductor module further includes a
wireless surface acoustic wave (SAW) temperature sensor disposed in the
housing of the power semiconductor module.

Claims:

1. A power semiconductor module, comprising: a housing; a base plate
disposed in the housing; a plurality of substrates mounted to the base
plate; a plurality of power transistor die mounted to the substrates; a
plurality of terminals mounted to the substrates and protruding through
the housing, the terminals in electrical connection with the power
transistor die; and a wireless surface acoustic wave (SAW) temperature
sensor disposed in the housing of the power semiconductor module.

2. A power semiconductor module according to claim 1, wherein the
wireless SAW temperature sensor is attached to the base plate.

3. A power semiconductor module according to claim 1, wherein the
wireless SAW temperature sensor is attached to one of the substrates.

4. A power semiconductor module according to claim 3, wherein the
substrate to which the wireless SAW temperature sensor is attached
comprises a ceramic material interposed between first and second
metallization layers, and the wireless SAW temperature sensor is attached
to one of the metallization layers.

5. A power semiconductor module according to claim 3, wherein the
substrate to which the wireless SAW temperature sensor is attached
comprises a ceramic material interposed between first and second
metallization layers, and the wireless SAW temperature sensor comprises
an interdigital transducer on a dielectric disposed on the ceramic
material of the substrate.

6. A power semiconductor module according to claim 1, wherein the
wireless SAW temperature sensor is attached to one of the terminals.

7. A power semiconductor module according to claim 1, further comprising
one or more additional wireless SAW temperature sensors disposed in the
housing.

8. A power semiconductor module according to claim 1, wherein the
wireless SAW temperature sensor is unpowered and operable to receive an
RF pulse signal and output an RF response signal as a function of the RF
pulse signal and a temperature of the wireless SAW temperature sensor.

9. A power semiconductor assembly, comprising: a power semiconductor
module comprising: a housing; a base plate disposed in the housing; a
plurality of substrates mounted to the base plate; a plurality of power
transistor die mounted to the substrates; a plurality of terminals
mounted to the substrates and protruding through the housing, the
terminals in electrical connection with the power transistor die; and a
wireless surface acoustic wave (SAW) temperature sensor disposed in the
housing of the power semiconductor module; a circuit board mounted to the
housing and having a plurality of electrical connectors which receive the
terminals protruding from the housing; and an RF transceiver circuit
mounted to the circuit board and configured to transmit RF pulses to the
wireless SAW temperature sensor and receive RF response signals generated
by the wireless SAW temperature sensor in response to the RF pulses.

10. A power semiconductor assembly according to claim 9, further
comprising a controller mounted to the circuit board and electrically
connected to the RF transceiver circuit, the controller configured to
convert the RF response signals received by the RF transceiver circuit to
temperature data.

11. A power semiconductor assembly according to claim 10, wherein the
controller is further configured to control operation of the power
semiconductor module based on the temperature data.

12. A power semiconductor assembly according to claim 10, wherein the
controller is further configured to report the temperature data to an
entity remote from the power semiconductor subassembly.

13. A power semiconductor assembly according to claim 10, wherein the
controller is remotely controllable from outside the power semiconductor
subassembly.

14. A power semiconductor assembly according to claim 10, wherein the
controller is configured to control an oscillator of the RF transceiver
circuit for generating the RF pulses.

15. A power semiconductor assembly according to claim 9, wherein the RF
transceiver circuit comprises an antenna disposed on the circuit board.

16. A power semiconductor assembly according to claim 15, wherein the
antenna is a wire or stripline formed as part of the circuit board.

17. A power semiconductor assembly according to claim 15, wherein the
antenna is spaced apart from the RF transceiver circuit by 10 cm or less.

18. A power semiconductor assembly according to claim 15, wherein the
antenna is spaced apart from the RF transceiver circuit by between 5 cm
and 10 cm.

19. A power semiconductor assembly according to claim 9, further
comprising one or more additional wireless SAW temperature sensors
disposed in the housing of the power semiconductor module.

20. A power semiconductor assembly according to claim 9, wherein the
wireless SAW temperature sensor is attached to one of the substrates.

Description:

TECHNICAL FIELD

[0001] The present application relates to power semiconductor modules, in
particular power semiconductor modules with temperature sensors.

BACKGROUND

[0002] Temperature measurement within IGBT (insulated gate bipolar
transistor) modules is typically realized using an NTC (negative
temperature coefficient) thermistor. NTC thermistors have isolation
requirements which require placement on a separate ceramic within the
module housing and connection to dedicated additional terminals. Such a
temperature sensor cannot be located closely to the most critical
elements of the system--the power transistors--and the measured
temperature data is less precise. Protective separation from the user
also is not inherently available with such temperature sensors because
NTC thermistors have externally accessible connection terminals. These
terminals can be inadvertently contacted during use, causing severe
electrical shock. Providing external isolation circuitry for reducing the
risk of electric shock adds to the overall package cost. Also, more space
is necessary for an NTC temperature sensor module and additional wire
connections are needed to provide electrical connections to the
temperature sensor. Extra electrical connections such as these reduce the
life time of the module.

SUMMARY

[0003] Temperature measurement within a power transistor module is
provided using a wireless SAW (surface acoustic wave) temperature sensor.
The SAW temperature sensor functions based on the piezoelectric effect.
Less space is needed for the SAW temperature sensor compared to
conventional NTC sensors since the SAW sensor does not require terminals
for inputting and outputting signals. Instead, communication with the SAW
sensor is wireless. This in turn provides more freedom to place the SAW
sensor in parts of the power transistor module not possible with
conventional NTC sensors. For example, measurement of the temperature
within the power transistor module can be made at the power terminal, at
the base plate on which power transistors are mounted via substrates, at
the substrates or at the power transistor die. The SAW temperature sensor
also provides intrinsic protective separation for reducing the risk of
electric shock, and no supply voltage within the module is needed for the
SAW sensor.

[0004] According to an embodiment of a power semiconductor module, the
module includes a housing, a base plate disposed in the housing, a
plurality of substrates mounted to the base plate, a plurality of power
transistor die mounted to the substrates, and a plurality of terminals
mounted to the substrates and protruding through the housing. The
terminals are in electrical connection with the power transistor die. The
power semiconductor module further includes a wireless surface acoustic
wave (SAW) temperature sensor disposed in the housing of the power
semiconductor module.

[0005] According to an embodiment of a power semiconductor assembly, the
assembly includes a power semiconductor module, a circuit board and an RF
transceiver circuit. The power semiconductor module includes a housing, a
base plate disposed in the housing, a plurality of substrates mounted to
the base plate, a plurality of power transistor die mounted to the
substrates, and a plurality of terminals mounted to the substrates and
protruding through the housing. The terminals are in electrical
connection with the power transistor die. The power semiconductor module
further includes a wireless SAW temperature sensor disposed in the
housing of the power semiconductor module. The circuit board is mounted
to the housing and has a plurality of electrical connectors which receive
the terminals protruding from the housing. The RF transceiver circuit is
mounted to the circuit board and configured to transmit RF pulses to the
wireless SAW temperature sensor and receive RF response signals generated
by the wireless SAW temperature sensor in response to the RF pulses.

[0006] Those skilled in the art will recognize additional features and
advantages upon reading the following detailed description, and upon
viewing the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

[0007] The elements of the drawings are not necessarily to scale relative
to each other. Like reference numerals designate corresponding similar
parts. The features of the various illustrated embodiments can be
combined unless they exclude each other. Embodiments are depicted in the
drawings and are detailed in the description which follows.

[0008] FIG. 1 illustrates a perspective view of an embodiment of a power
semiconductor assembly including a power semiconductor module with a
wireless SAW temperature sensor.

[0009]FIG. 2 illustrates an embodiment of a wireless SAW temperature
sensor and corresponding controller and RF transceiver circuit for
actuating and sensing the SAW sensor.

[0010]FIG. 3 illustrates a perspective cross-sectional view of another
embodiment of a power semiconductor assembly including a power
semiconductor module with a wireless SAW temperature sensor.

[0011]FIG. 4 illustrates a perspective view of an embodiment of a power
semiconductor module with a wireless SAW temperature sensor.

[0012]FIG. 5 illustrates a perspective view of an embodiment of a
substrate with a wireless SAW temperature sensor included in a power
semiconductor module.

[0013]FIG. 6 illustrates a perspective view of another embodiment of a
substrate with a wireless SAW temperature sensor included in a power
semiconductor module.

[0014]FIG. 7 illustrates a perspective view of another embodiment of a
power semiconductor module with a wireless SAW temperature sensor.

DETAILED DESCRIPTION

[0015] FIG. 1 illustrates an embodiment of a power semiconductor assembly
100. The assembly 100 includes a circuit board 110 and a power
semiconductor module 120. Various active and passive components such as
resistors, capacitors, inductors, power transistors (e.g. IGBTs), diodes,
terminals, etc. are enclosed within the housing 121 of the power
semiconductor module 120 and not visible in FIG. 1. Also included in the
module housing 121 are one or more wireless surface acoustic wave (SAW)
temperature sensors 122. One SAW sensor 122 is shown in FIG. 1 with a
dashed box, but any desired number of SAW sensors can be enclosed in the
module housing 121 for gathering temperature data about the power
semiconductor module 120.

[0016] The circuit board 110 is mounted to the housing 121 of the power
semiconductor module 120, although FIG. 1 shows the circuit board 110
e.g. a PCB (printed circuit board) detached from the module housing 121
for ease of illustration of the various assembly components. Components
such as semiconductor die, passive elements, wiring traces, etc. are
provided on and/or in the circuit board 110 and ensure proper operation
of the power transistors contained inside the power semiconductor module
120 and are not shown in FIG. 1 for ease of illustration. The circuit
board 110 also has a plurality of electrical connectors 112 for receiving
terminals 124 protruding from the power module housing 121. Some
terminals 124 protruding from the module housing 121 may be for control
signals while other terminals 126 are power terminals.

[0017] An RF transceiver circuit 114 is also mounted to the circuit board
110. The RF transceiver circuit 114 and a corresponding antenna 116 are
shown with dashed lines in FIG. 1 because these components are mounted to
the bottom side of the circuit board 110 which faces the power
semiconductor module 120 and therefore are out of view. The antenna 116
can be a wire or stripline formed as part of the circuit board 110. In
one embodiment, the antenna 116 is spaced apart from the wireless SAW
temperature sensor 122 by 10 cm or less, e.g. by between 5 cm and 10 cm.
The RF transceiver circuit 114 and/or antenna 116 can instead be mounted
on the top side of the circuit board 110 if desired.

[0018] In each case, the RF transceiver circuit 114 transmits RF pulses to
the wireless SAW temperature sensor 122 via the antenna 116 and receives
RF response signals generated by the wireless SAW temperature sensor 122
in response to the RF pulses. The RF response signals received at the RF
transceiver circuit 114 are converted to temperature data which can be
used to control operation of the power semiconductor module 120. For
example, the temperature data can be reported to an entity remote from
the power semiconductor subassembly 100 for use in remotely controlling
operation of the module 120. The temperature data can be used to safely
shut down one or more transistors included in the power module 120 if the
temperature data indicates a problem e.g. if a maximum permitted
temperature is exceeded.

[0019]FIG. 2 illustrates the RF transceiver circuit 114 and wireless SAW
temperature sensor 122 in more detail. The wireless SAW temperature
sensor 122 is unpowered and receives an RF pulse signal 200 from the RF
transceiver circuit 114. The SAW sensor 122 outputs an RF response signal
202 as a function of the RF pulse signal 200 received from the RF
transceiver circuit 114 and the temperature of the SAW sensor 122.

[0020] The wireless SAW temperature sensor 122 includes an interdigital
transducer 204 (or interdigital transformer, or IDT for short) connected
to a sensor antenna 206 plus several reflectors 208 formed on the surface
of a material 210 which exhibits elasticity such as a piezoelectric
material like quartz, lithium niobate, lithium tantalate, lanthanum
gallium silicate, etc. The IDT 204, which is enlarged in FIG. 2, includes
electrode structures 212, 214 in the form of fingers 216, 218 connected
to each other. The distance between two adjacent fingers 216/218
connected to the same electrode 212/214 is labeled `p` in the enlarged
view of the IDT 204. These two fingers 216/218 are at the same potential
and have an electrical period labeled `q` in the enlarged view of the IDT
204.

[0021] In response to an AC voltage applied to the electrode structures
212, 214, the surface of the SAW sensor 122 deforms based on the
piezoelectric effect. This deformation causes an acoustic wave which
propagates through and/or on the surface of the SAW sensor 122. Any
changes to the characteristics of the propagation path affect the
velocity and/or amplitude of the wave, which is reflected back to the IDT
204 by the reflectors 208. The reflectors 208 can be replaced by a second
IDT which can be used to receive the propagation wave. In either case,
changes in velocity can be monitored by measuring the frequency and/or
phase characteristics of the SAW sensor 122 and can then be correlated to
the corresponding physical quantity being measured e.g. temperature. In
the opposite manner, an incoming wave on the surface of the SAW sensor
122 yields an AC voltage at the electrode structures 212, 214.

[0022] A temperature change at the SAW sensor 122 influences the
propagation speed of the wave through/over the surface of the
piezoelectric material 210 and therefore influences the overall
electrical behavior of the SAW sensor 122. A signal with high frequency
meets the SAW sensor 122 and the resulting surface acoustic wave changes
depending on the temperature in altitude and phase lag. A controller 230
can interpret this signal received from the SAW sensor 122 to derive the
corresponding temperature data. The SAW sensor 122 has a dedicated
frequency band of operation and a defined relationship between output
frequency and temperature. The controller 230 can use this information
along with the characteristics of the RF pulse signal 200 transmitted to
the SAW sensor 122 to convert the corresponding RF response signal 202
received from the SAW sensor 122 into temperature data.

[0023] The controller 230 also controls operation of the oscillator 232
(e.g. a numerical controlled oscillator, or NCO for short) provided as
part of the RF transceiver circuit 114. The NCO 232 drives an RF
transmitter 234 in order to periodically generate an RF pulse signal 200
directed to the SAW sensor 122 via the antenna 116 connected to the RF
transceiver circuit 114. A switch 236 such as a duplexer connects the
antenna 116 to either the transmitter 234 (for transmitting the RF pulse
200 to the SAW sensor 122) or a receiver 238 for receiving the
corresponding RF response signal 202 from the SAW sensor 122. A distance
of 10 to 15 m can exists between the polling RF pulse signal 200 and the
corresponding received RF response signal 202. The controller 230 can be
a discrete component e.g. on a driver board or be integrated in the
module control unit which controls overall operation of the power
semiconductor module 120, or in a frequency converter or servo drive
circuit. If integrated as part of the system control circuit, the
controller 230 can aid in the control of the power semiconductor module
120 based on the temperature data. The controller 230 can also report the
temperature data to an entity remote from the power semiconductor
subassembly e.g. via an Internet or wireless connection. Similarly the
controller 230 can be remotely controlled from outside the power
semiconductor subassembly.

[0024]FIG. 3 illustrates another embodiment of a power semiconductor
assembly 300. According to this embodiment, at least some of the
terminals protruding from the power semiconductor module 120 are
press-fit connectors 302 which are press-fit into corresponding
electrical connectors 304 in the circuit board 110. A fastener 306 such
as a screw or bolt can be used to fasten the circuit board 110 and the
power semiconductor module 120 to a heat sink 308. One or more wireless
SAW temperature sensors 122 are disposed within the module 120 as
indicated by the dashed box. The RF transceiver circuit 114 and antenna
116 are shown disposed on the surface of the circuit board 110 facing
away from the module 120. The RF transceiver circuit 114 and/or antenna
116 alternatively can be positioned on the opposite side of the circuit
board 110 if desired.

[0025]FIG. 4 illustrates an embodiment of the power semiconductor module
120 with the housing 121 removed. The module 120 includes a base plate
400 disposed in the housing 121, a plurality of substrates 402 mounted to
the base plate 400, a plurality of power transistor die 404 such as IGBT
die mounted to the substrates 402 and a plurality of terminals 406
mounted to the substrates 402. The terminals 406 protrude through the
module housing 121 e.g. as shown in FIGS. 1 and 2. The terminals 406 are
in electrical connection with the power transistor die 404 e.g. via
patterned metallization layers 408 disposed on the substrates 402 and
bonding wires, ribbons, etc. 410 connecting the patterned metallization
layers 408 to the die 404. One or more wireless SAW temperature sensors
122 are also disposed in the housing 121 of the power semiconductor
module 120.

[0026] According to the embodiment illustrated in FIG. 4, the SAW
temperature sensor 122 is attached to the base plate 400. For example,
the sensor 122 can be soldered or glued to the base plate 400. A low
temperature joining technology or diffusion soldering process can be
employed to attach the SAW sensor 122 to the base plate 400. Other sensor
attach processes may also be used. The temperature sensed by the SAW
sensor 122 corresponds to that of the base plate 400 in this embodiment.
The SAW temperature sensor 122 can be located in a different position, or
additional SAW temperature sensors 122 can be provided at other locations
within the module housing 121 to measure different temperatures.

[0027]FIG. 5 shows an embodiment of one of the substrates 402 included in
the module housing 121 with a wireless SAW temperature sensor 122
attached to the substrate 402. According to this embodiment, the
temperature sensed by this SAW sensor 122 corresponds to that of the
substrate 402. In one embodiment, the substrate 402 to which the wireless
SAW temperature sensor 122 is attached comprises a ceramic material 500
interposed between a top metallization 408 and a bottom metallization
which is out of view in FIG. 5. The wireless SAW temperature sensor 122
is attached to one of the metallizations e.g. via glue, solder, etc. In
FIG. 5, the SAW sensor 122 is attached to the top metallization 408 of
the substrate 402. Examples of suitable ceramic materials 500 for use in
the substrate 402 include aluminum nitride (AlN), aluminum oxide,
(Al2O3), silicon nitride (Si3N4), silicon carbide
(SiC), or beryllium oxide (BeO). The metallizations can comprise copper
or a copper alloy having a high proportion of copper. The substrate 402
can be, for example, a DCB substrate (DCB=Direct Copper Bonding), a DAB
substrate (DAB=Direct Aluminum Bonding), an AMB substrate (AMB=Active
Metal Brazing), etc.

[0028]FIG. 6 shows another embodiment of one of the substrates 402
included in the module housing 121 with a wireless SAW temperature sensor
122 attached to the substrate 402. According to this embodiment, a
dielectric material 502 such as SiO2 is disposed on the ceramic material
500 of the substrate 402 and the SAW sensor 122 is disposed on the
dielectric material 502. Alternatively the SiO2 layer can be realized on
the metallization at the bottom side of the substrate 402 which is out of
view in FIG. 6 and the SAW sensor 122 can be soldered or glued to the
base plate 400 in this region of the substrate 402 e.g. in a recess
formed in the base plate 400 so that the substrate 402 contacts the base
plate 400 in a planar manner.

[0029]FIG. 7 shows an embodiment of the power semiconductor module 120
without the housing 121 and with a wireless SAW temperature sensor 122
attached to one of the terminals 406 of the module 120. In one
embodiment, this SAW sensor 122 is attached to the main power terminal of
the module 120 e.g. the terminal connected to the drains of the power
transistor die 404 included in the module 120. The SAW sensor 122 can be
glued or soldered to the terminal 406 and the temperature sensed by this
SAW sensor 122 corresponds to that of the terminal 406 which in turn
correlates to the amount of current flowing in the power transistor die
404.

[0030] Spatially relative terms such as "under", "below", "lower", "over",
"upper" and the like, are used for ease of description to explain the
positioning of one element relative to a second element. These terms are
intended to encompass different orientations of the device in addition to
different orientations than those depicted in the figures. Further, terms
such as "first", "second", and the like, are also used to describe
various elements, regions, sections, etc. and are also not intended to be
limiting. Like terms refer to like elements throughout the description.

[0031] As used herein, the terms "having", "containing", "including",
"comprising" and the like are open ended terms that indicate the presence
of stated elements or features, but do not preclude additional elements
or features. The articles "a", "an" and "the" are intended to include the
plural as well as the singular, unless the context clearly indicates
otherwise.

[0032] It is to be understood that the features of the various embodiments
described herein may be combined with each other, unless specifically
noted otherwise.

[0033] Although specific embodiments have been illustrated and described
herein, it will be appreciated by those of ordinary skill in the art that
a variety of alternate and/or equivalent implementations may be
substituted for the specific embodiments shown and described without
departing from the scope of the present invention. This application is
intended to cover any adaptations or variations of the specific
embodiments discussed herein. Therefore, it is intended that this
invention be limited only by the claims and the equivalents thereof.